The invention relates to x-ray tubes used in medical imaging. In particular, the invention relates to a method and apparatus for adjusting a filament set height in a cathode cup assembly for an x-ray tube.
An x-ray source is often used in medical imaging systems, such as, but not limited to, computed tomography, fluoroscopy and mammography systems. The x-ray source typically includes an evacuated vessel, known as the frame, containing an anode and a cathode. X-rays are produced by applying a high voltage across the anode and cathode, and accelerating electrons from the cathode toward a focal track on the anode.
Known cathode assemblies for such x-ray sources typically include a cathode cup and a plurality of current carrying filaments. The filament leads extend through the cup via the filament feed-through assembly, which typically comprises an electrical insulator and a metallic sleeve used for securing the leads at the desired location.
At least one known filament geed-through assembly includes a tubular filament post, a substantially cylindrical insulator, and a sleeve. The filament post may be positioned within the sleeve. Precise positioning of the filaments with respect to the cathode cup is important because the positioning affects operational characteristics of the x-ray tube, such as the focal spot size and position and the emission current. Accordingly, it is desirable to properly position the filament leads and thus the filament within the cathode cup.
Conventional filament setting methods for adjusting the filament set height may use pliers and a hammer to pull, twist, or push the filament lead to its desired location. The extent of lead movement is difficult to control, and the desired filament alignment is attained by iteratively adjusting and measuring the filament position, until the filament set height is within a desired tolerance. This process is time-consuming and requires multiple steps to position the filament within the desired filament set height tolerance and may result in damage to the filament assembly.
Accordingly, a need exists to enhance the filament setting operations. In particular, a need exists for adjusting filament positions in cathodes and similar devices.
An aspect of the invention provides a method for adjusting a filament set height in a cathode of an x-ray tube. The method for adjusting a filament set height in a cathode comprises providing a cathode cup of an x-ray tube, the cathode cup comprising at least two feed-throughs extending therethrough; inserting a filament lead through the at least two feedthroughs to a filament set height below a desired filament set height; measuring an actual filament set height that results from the step of inserting; comparing actual filament set height that results from the step of inserting to the desired filament set height; determining an adjustment to the filament set height in which the adjustment is generally equal to a difference between the actual filament set height and the desired filament set height; contacting an end of the filament post with an adjustment tool; and moving the adjustment tool a distance substantially equal to said adjustment filament set height distance. Therefore, the filament is positioned at the predetermined filament set height.
A further aspect of the invention provides a device for adjusting a filament set height of a filament in a cathode. The device comprises a fixture comprising a central bore having a first open end and a second open end; an axial calibrator received in the first open end of the fixture and disposed relative to the second open end; and a clamp adjacent the second open end for securing the fixture to a portion of the cathode such that a filament post extends through the second opened end and is capable of being moved along its axis. The calibrator is capable of being brought into contact with an end of the filament lead.
Another aspect of the invention sets forth an adjustment apparatus for adjusting an x-ray tube filament. The adjustment apparatus comprises a fixture, a central bore having a first open end and a second open end; a micrometer received in the first open end of the fixture and disposed relative to the second open end; and a clamp adjacent the second open end for securing the fixture to a portion of the cathode such that a filament lead of the filament extends through the second opened end. The micrometer is capable of being brought into contact with an end of the filament post and adjusting the position of the filament post so as to affect the filament set height.